Electron discharge device of the magnetron type



April 3, 1951 J. BARTTRO ELECTRON DISCHARGE DEVICE OF THE MAGNETRON TYPE Filed Jan. 8, 1949 INVENTOI? JAMES L. BARTTRO ATTORNEY Patented Apr. 3, 1951 UNITED STATES PATENT OFFICE.

ELECTRON DIS CHARGE DEVICE OFTHE MAGN'ETRON' TYPE James L. Barttro, Watertow-n, Mass assig-nor to Raytheon Manufacturing Company, New-ton, 'Ma'ss., a corporation of'Delaware Application January 8, 1949, SerialNo. 69,919

'4. claims.

This application relates to electron discharge members are always at equal potential, known as the 1r mode-of operation. However, due-to a heavy loading-of this 1r mode by the device being fed by the magnetron and due to variations in themagnetic field, andin the anodesvoltage of the .dev-ice, the'magnetron will sometimes .begin to operate in the mode of the next higher frequency above-the 1rmode frequency, since this mode is substantially unloaded bylthe apparatus to whichthe magnetronis coupled.

Itis believed that when a magnetron is turned on the first oscillations in any mode build up due to the sporadic noise disturbances, enhanced by a major' or minor, geometricallyecaused, resonance occurring at the frequency of the mode.

Therefore, it is an object of this invention {to damp out the noise frequencies-at the undesired mode of operation thereby suppressing operation in this mode.

A further object of this invention is to load the undesired mode ofoperation thereby absorbing. the power from this undesired modejof operation andpreventing substantial building up of oscillations in the same.

Other and further objects of this invention will becomeapparcnt as the description thereof progresses, reference being had: to the accompanying drawing wherein: V

Figjl is' a vertical cross-sectional viewyta'lren along line l--| of Fig. 2, of a magnetron built, in accordance with this invention; and

Fig.2 is a horizontal cross-sectional view taken along line 2-2 of Fig. 1.

Referring now to Figs. 1 and 2 there is shown a magnetron comprising a heavy cylindrical member Ill which may be of copper, whose ends are closed by fiat, round disks 1 l which are sealed thereto as by soldering. Extending radially inwardly from the inner surface of the cylindrical member It! are a plurality of rectangular-shaped anode members i2. Each pair of adjacent anode members together with the space therebetween define a cavity which basically determines the frequency of operation of the device. The anode members I2 do not extend completely to the center of the cylindrical member ill, but rather leave a cylindrical hole in which is positioned a cathode structure I3. This cathode structure 2. comprises a cylinder, the outer surface of which is coated with electron-emissive material, which is heated by a coil inside said cylinder. The details of this cathode structure are more specifically set forth in Patent No. 2,439,786, issued April 20, 1948. The cathode structure [3 is supported by a pair of leads I 4 attached to the cathode structureat each end thereof and which extend out through the wall of the cylinder It through a pair of insulating seals [5 whereby'an external heater voltage may be applied to heat the cathode,

and an external potential may be applied-between the cathode and anode. The magnetic pole pieces iii of the magnetron are applied ad jacent the end plates H to produce the required magnetic field-across the inter-action spaces between the cathode I3 and the anode members [2 in a well-known manner.

In order to prevent operation of the magnetron in amodelower than the 1r mode and to increase the separation of the 'n' mode from the higher modes, a-pair of straps I! are connected to alternate anode members'on the bottom edge thereof and toward the inner ends thereof and a similar pair of straps is. attached tothe top edges. The action of these straps is well known andmore fullydisclosedby Patent No. 2,4l7,'7.89, issued March 18, 1947.

Powjeris fedtto the load by meansof an antenna coupling loop i8, one end of which is attached. to the cylinder l0 and the other-endsof which passes though a seal l9 inthe cylinder and thence to the load.

. In order to suppress oscillations at the frequency of. the next higher mode above the 11' mode, a wire 20 is attached to oneof the vanes at a. point which is substantially a .voltage node fonth'e modeabove the 1: mode. This wire extends from the vane upwardly into a receptacle 2i of some lossy substances such as carbon or finely divided iron particles in a suitable binder such as clay. This receptacle is in turn attached to the cylinder H3. The length of the wire 20 between its point of attachment on the vane I2 and the receptacle 2! is made substantially equal to a quarter wave length of the frequency of the mode which it is desired to suppress; namely, the mode above the 1r mode.

Since the wire 2E5 is attached to a voltage node for the mode to be suppressed, the point at which the wire 28 enters the receptacle 2! will be a high current point for the frequency of the mode to be suppressed. This high current will pass through the receptacle 2| to the anode cylinder it which is at R. F. ground potential, thereby dissipating a large amount of power in the lossy material 2|. Since this power being dissipated would normally have remained in the cavities thereby building up oscillations at the undesired frequency, the dissipation of this power in the lossy substance 2| suppresses oscillations in the undesired mode.

Obviously the Q of the dissipating circuit comprising the vane l2, the wire 20, the lossy material 2| and the anode cylinder Ill must be high enough such that it will pass substantially no power from the 1r mode of frequency into the lossy material 2!.

In a strapped magnetron of this type having twenty anode members, the mode separation will be as much as 30% and therefore the Q of the dissipated circuit could be as low as three for this particular application without appreciably sapping power from the 11' mode of operation.

It is to be clearly understood that while I have shown only one wire 20 feeding undesired oscillations to the lossy material 2| from one of the vanes I2, more wires 20 may be attached to other vanes l2 to further increase the power-suppressing capacity of the lossy material 2| for the undesired frequency. Moreover, other wires 29 could be tuned to higher modes above the first mode above the 1: mode to prevent operation in said higher modes.

This completes the description of one modification of the invention. However, many other modifications will be apparent to those skilled in the art. For example, the wire 20 might be in the form of a probe and might be some multiple of a quarter wave length other than one, or might be fed from a current node rather than a voltage node. Also, it is not necessary that the straps ll be used on the vanes and indeed other configurations of the anode structure may be used without departing from the spirit and scope of the invention. Therefore, applicant desires a broad interpretation of the appended claims commensurate with the scope of the invention within the art.

What is claimed is:

1. An electron discharge device comprising an evacuated envelope containing a cathode and a plurality of anode members radially spaced from said cathode, adjacent anode members together with the space therebetween defining resonant cavities, and means for suppressing oscillations at frequencies, other than that at which each of said cavities is primarily resonant, comprising a wire Whose electrical Wave length is a multiple of a quarter wave length of the frequency to be suppressed coupled to said cavities and to a power dissipation means. 7

2. An electron discharge device comprising an evacuated envelope containing a cathode and a plurality of anode members, adjacent anode mem: bers together with the space therebetween defining resonant cavities, means for producing a magnetic field perpendicular to the electron path between said cathode and said anode, and means for suppressing oscillations at frequencies, other than that at which each of said cavities is primarily resonant, comprising a wire whose electrical wave length is a multiple of a quarter wave length of the frequency to be suppressed coupled to said cavities and to a power dissipation means, said wire being attached to a voltage node, of the frequency to be suppressed, on one of said anode members.

3. An electron discharge device comprising an evacuated envelope containing a cathode and a plurality of anode members, adjacent anode members together with the space therebetween defining resonant cavities, means for directing electrons from said cathode to said anode along modified circular paths, and means for suppressing oscillations at frequencies, other than that at which each of said cavities is primarily resonant, comprising a wire whose electrical wave length is a multiple of a quarter wave length of the frequency to be suppressed coupled to said cavities and to a power dissipation means, said power dissipation means comprising a mass of carbon.

4. An electron discharge device comprising an evacuated envelope containing a cathode and a plurality of anode members, adjacent anode members together with the space therebetween defining resonant cavities, means for controlling the flow of electrons from said cathode to said anode comprising means for producing a magnetic field, and means for suppressing oscillations at frequencies, other than that at which each of said cavities is primarily resonant, comprising a wire whose electrical wave length is a multiple of a quarter wave length of the frequency to be suppressed coupled to said cavities and to a power dissipation means, said wire being attached to a voltage node of the frequency to be suppressed on one of said anode members and said power dissipation means comprising a mass of carbon.

JAMES L. BARTTRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,422,028 Martin June 10, 1947 2,422,695 McRae June 24, 1947 2,424,576 Mason July 29, 1947 2,446,572 Bull Aug. 10, 1948 2,504,329 Heising Apr. 18, 1950 

